Hitherto, there has been a monitoring system including a plurality of monitoring cameras and configured to transmit image data taken by each monitoring camera to a server. Further, there has been a technology that allows the monitoring system to record the image data that is an imaging result and transmit the image data to the server only in a case where the monitoring camera detects a specific event (detects suspicious persons, for example), to thereby achieve power saving (see, for example, PTL 1).